<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>三栏布局</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    .box{
      display: flex;
    }
    .left{
      width: 200px;
      height: 600px;
      background:pink;
    }
    .middle{
      flex: 1;
      height: 600px;
      background-color: rgb(139, 209, 92);
    }
    .right{
      width: 200px;
      height: 600px;
      background-color: skyblue;
    }
  </style>
</head>
<body>
  <div class="box">
    <div class="left">

    </div>
    <div class="middle">

    </div>
    <div class="right">

    </div>
  </div>
</body>
</html>